I've found a solution that worked for us.
H-> Host
J-> 2nd player
1. H have to stay at direct X11 at all times
2. H loads the game then moves all characters to one party, dismisses all summons, go to camp with all characters.
3. H starts a conversation with NPC with main character of J.
4. J load game with direct X11.
5. J joins by steam friend list.
6. J leaves camp.
7. J TP with any kind of portals/doors/etc. that changes location.
8. J Bug appear (Missing walls, no walking animations, T-pose NPC)
9. J Using portals/doors/etc. that changes location ONCE MORE to stay at loading then alt + F4
10. J launches the game with Vulcan
11. If white screen at the start, WAIT. Do not click anything, just wait (this one took us 8 minutes - I guess the time could be lower, depends on pc)
12. J Joins by steam friend list when H chooses the dialog option.
12a. When J loads his character MUST BE MID dialog.
13. J might have graphic Artifacting - when loaded wait until (in our case black squares) they disappear.
14. Fixed
Now you can move 2nd character to your partner.
I don't know if it'll help everyone - it helped us.
Location where we ungliched (spoilers ahead):
We did it in Ramazith's Tower.
Who we talked with (spoilers ahead):
Lorroakan post talking with Dame Aylin telling her the truth
